Plate Tectonics: Earth’s Dynamic Crust and Seismic Activity

Posted on Jan 6, 2025 in Geology

**Borders Neutral**

Borders neutral: Only collide and slide; therefore, the lithosphere is neither created nor destroyed. They can have volcanism. Example: San Andreas Fault.

**Tapering Edges**

Tapering edges: Also called destructive edges. The oceanic crust is destroyed. Their types are:

  • Ocean-continent: The oceanic crust is introduced into the continental crust, which makes mountains climb (Andes).
  • Ocean-ocean: The oceanic crust is introduced into a mixed crust (Japan).
  • Continent-continent: Both are mixed. Neither can be put above the other, so the terrain does not rise.

**The Wilson Cycle of Plate Evolution**

The evolution of plate, Wilson cycle “phase”

  • Fragmentation: Continental mantle materials produce the abandonment until they break because of their rigidity. The fractures help the magma to exit.
  • Close oceanic gulf: The expansion of an ocean floor forms a narrow sea (Red Sea and Gulf of Aden).
  • Ocean basin with stable continental magmas: The growth of the ocean floor allows the development of an ocean basin (Atlantic and Indian). In its bottom, there is a deposit of sediments.
  • Reducing ocean basin: The stable continental magmas become active when the lithosphere sinks at subduction (Pacific). It may be related to the density of rocks.
  • Close oceanic basin: The reduction of the ocean is clear; marginal ridges are formed.
  • Stage closure of the ocean basin: The sinking of the subducted lithosphere and the ocean is closed, continents collide, and an intracontinental mountain is created (Himalaya).

**Evidence of Plate Tectonics**

Evidence of plate tectonics

  • Paleontological Evidence:
    1. Existence of similar plant and animal fossils between Africa and South America.
    2. Physiographic coincidence between the coasts of Africa and South America.
    3. Geological studies of rocky mountain ranges.
    4. Alignment of very geographically separated structures.
  • Tests: Alignment of mountain ranges widely separated in the present. Physiographic coincidence between the coasts of Africa and South America. The coincidence is greater if done from tests based on seismic sources: volcanic and seismic zones in the most important areas of the planet. If we join seismic and volcanic zones, we obtain the limits (edges).

**Claims of Plate Tectonics**

Claims of plate tectonics

  1. The lithosphere is divided into large blocks called plates that cover all the land surface and fit together like pieces of a puzzle.
  2. Most of the internal geological activity (volcanoes, earthquakes, deformation) occurs at the edges or boundaries between plates. Inside, this activity is scarce.
  3. The oceanic lithosphere, thinner and denser than the continental, is generated continuously at the ocean ridges and is destroyed in the trenches.
  4. The plates are moving, dragging the continents with them and interacting with each other.

**Earthquakes**

Earthquakes: Earthquakes are vibrations or earthquakes of varying intensity that occur when energy is released abruptly and rapidly. Earthquakes originate in volatile areas of the crust and, in particular, the limits of the plates. The point inside the earth where the earthquake originates is called the seismic focus or hypocenter. The surface projection on the seismic focus is called the epicenter.

**Elastic Rebound**

Elastic Rebound: The mechanism that causes most earthquakes is elastic rebound: as the rocks are deformed, they continuously store elastic energy. If the rocks are deformed above their endurance limit, they suddenly burst and release the stored energy, producing vibrations (seismic waves).

**Volcanoes and Their Activity**

Volcanoes and their activity: A volcano is a geological structure through which magmas rise to the surface of the crust or mantle.

  • Fissural Volcanoes: When the magma rises through fractures as long as 25 km long.
  • Central Volcanoes: Are those in which the magma rises through a point on the crust.

**Classification of Volcanoes**

Classification of volcanoes:

  • Volcano Type: Pelean
    • Magma Composition: Rich in silica and gases (acids)
    • State of Magma: Very viscous
    • Rocks: Clear minerals (Rhyolite)
    • Eruption: Violent (pyroclastics)
  • Volcano Type: Composite or stratovolcano
    • Magma Composition: Intermediate
    • State of Magma: Intermediate
    • Rocks: Andesites
    • Eruption: Alternating pyroclastic and lava flows
  • Volcano Type: Shield or Hawaiian
    • Magma Composition: Poor in silica and gases (core)
    • State of Magma: Molten, fluent
    • Rocks: With dark minerals (basalts)
    • Eruption: Quiet (lava flow)

**Factors to Form Magma**

Factors to form magma

  • Increased temperature
  • Decreased pressure
  • Presence of substances that reduce the melting point
  • Existence of cracks, fractures, or exit routes

**Volcanism in Spain**

Volcanism in Spain: Canary Islands, Ciudad Real, Alboran Island, Almeria and Murcia, Columbretes Islands, Girona.